In recent years light-emitting electrochemical cells (LEECs) utilizing ionic transition metal complexes (iTMCs) as luminophores1 have been attracting considerable interest in the area of solid-state lighting. One of the most popular species of iTMCs in LEECs are cationic iridium(III) complexes of the form [Ir(C^N)2(N^N)]PF6 (C^N is a cyclometalating ligand, N^N is a diimine ancillary ligand).
Excited state self-quenching during the operation can limit the lifetime of the device. A strategy to circumvent this issue is to decorate the Ir-complexes with bulky, hydrophobic substituents that increase the intermolecular distance while also hindering the disadvantageous attack of small molecules. For example, introduction of bulky substituents on the N^N ligand leads to more stable LEECs.2,3
In this context, we will present a new family of cationic Ir(III) complexes [Ir(C^N)2(dtBubpy)]+ in which bulky substituents R1 and R2 have been incorporated onto the C^N ligands. We will show the impact of the steric bulk on their photophysical, electrochemical, and photoluminescence properties.

Organic Light Emitting Diodes (OLEDs) represent the next generation visual displays and lighting. Thanks to the highly efficient intersystem crossing (ISC) present in many organometallic emitters, phosphorescent OLEDs can achieve much higher internal quantum efficiencies than their fluorescent analogues due to recruitment of triplet excitons. However, most of these organometallic emitters are made of expensive and rare metals such as iridium and platinum.

Recently, Adachi and co-workers have developed small molecular organic emitters that operate via a thermally activated delayed fluorescence (TADF) mechanism that address the aforementioned issues.[1-3] These organic emitters can also harvest both singlet and triplet excitons.
Compared with OLEDs, light-emitting electrochemical cells (LEECs) enjoy the advantages of using an air-stable cathode, are operated at lower potentials and possess a simpler single-layered device structure, all of which immensely reduce the cost of industrial OLED fabrication. Typically the emitters in LEECs is an ionic transition metal complex based primarily on iridium(III). In this work we illustrated how small molecular charged organic emitters, MYW-1 and MYW-2, operating through TADF are compatible in LEECs and we also present solution-processed OLED data.

Palladium complexes are versatile catalysts in the synthetic chemistÕs arsenal, but have been overlooked by materials chemists as they exhibit disappointing optoelectronic properties compared to their platinum analogues; despite the full d-shell makes population of MC states impossible, Pd(0) complexes reported thus far are very poorly luminescent.

In this work we show, as a proof of concept, the first examples of highly luminescent ditopic Pd(0) complexes. These complexes demonstrate unprecedented photophysics, with the highest PLQY for any palladium materials reported, and tunable emission. We rationalize these properties using a combination of spectroscopic and theoretical techniques, and report the first working OLEDs adopting a Pd(0) complex as the emissive material.

ISPPCC 2015 , 07/05/2015-07/09/2015, Krakow, Poland

Impact of the Use of Sterically Congested Luminescent Iridium(III) Complexes on the Performance of LEECsView PDF

In recent years light-emitting electrochemical cells utilizing ionic transition metal complexes as luminophores [1] have been attracting considerable interest in the area of solid-state lighting. One of the most popular families of emitters are [Ir(C^N)2(N^N]PF6 complexes (C^N is a cyclometalating ligand, N^N is a diimine ancillary ligand). Excited state self-quenching during the operation can limit the lifetime of the device. A strategy to circumvent this issue is to decorate the complexes with bulky, hydrophobic substituents that increase the intermolecular distance while also hindering the disadvantageous attack of small molecules; addition of bulky groups on the N^N ligands has resulted in more stable LEECs [2, 3].

In this context, we will present a new family of cationic Ir(III) complexes [Ir(C^N)2(dtBubpy)]+ in which bulky substituents R1 and R2 have been incorporated onto the C^N ligands. We will show the impact of the steric bulk on their photophysical, electrochemical, and most importantly, electroluminescent properties.

C.H. acknowledges the Royal Society of Chemistry for a financial support.

In the last few years, significant effort has been made to develop blue phosphorescent iridium-based emitters, especially for lighting and display applications. Despite many blue-emitting iridium (III) complexes having been explored, current challenges still remain regarding the efficiencies and stabilities of such emitters in devices. Perhaps surprising, given their common use as ligands in organometallic catalysis, phosphorous-based chelators have been little investigated in cyclometalated iridium (III) systems [1-3].

Herein we present a structure-property relationship study of thirteen cationic iridium (III) complexes of the form of [(C^N)2Ir(P^P)]PF6 in both solution and the solid state through systematic evaluation of six bisphosphine (P^P) ligands. By optimizing the bite angle of the P^P chelate and coupling it with bulky C^N ligands, bright blue emitters have been obtained.

Iridium(III) complexes have been widely investigated as emissive materials owing to their exceptional photophysical properties, which include: emission tuning across the visible spectrum as a function of ligand type, generally high photoluminescence quantum yields and short radiative lifetimes for a phosphorescent emitter. Despite this large interest, reports exploring their use as light-harvesting materials remain scarce, particularly owing to the difficulty in modulating their absorption profiles further to the red part of the visible spectrum. In this poster, I will present our recent efforts to develop panchromic absorbing iridium(III) materials and discuss their compatibility as dyes in dye-sensitized solar cells (DSSCs) and organic photovoltaics (OPVs).

The expansion of low-cost and more efficient lighting sources is one of the greatest challenges of our century. In the last decade, despite many green and red phosphorescent emitters having been employed for solid-state lighting, the design of high efficient blue-emitting iridium-based materials, especially for lighting and display applications, is still far for being mature. Recently, many blue-emitting cyclometalated iridium (III) complexes bearing bi(imidazole), substituted triazole or tetrazole and bis(NHC)s as ancillary ligands have been explored, but current challenges still remain regarding the efficiencies and stabilities of such emitters in devices. Perhaps surprisingly, given their common use as ligands in organometallic catalysis, phosphorous-based chelators have been little investigated in cyclometalated iridium (III) systems.[1-3]
Herein we present a structure-property relationship study of thirteen cationic iridium (III) complexes of the form of [(C^N)2Ir(P^P)]PF6 in both solution and the solid state through systematic evaluation of six common bisphosphine (P^P) ligands, such as xantphos, dpephos, dppe, Dppe, isopropxantphos and nixantphos. Our results show that by optimizing the bite angle of the P^P chelate and coupling it with bulky cyclometalating C^N ligands, bright blue emitters with high phosphorescent quantum yields and long-lived triplet excited states can be obtained (Figure 1). Light-Emitting Electrochemical Cells (LEECs) and Organic Light-Emitting Diodes (OLEDs) have been fabricated using lead complexes from this study and their performances in device have been investigated.

In recent years light-emitting electrochemical cells (LEECs) utilizing ionic transition metal complexes (iTMCs) as luminophores [1] have been attracting considerable interest in the area of solid-state lighting. One of the most popular species of iTMCs in LEECs are cationic iridium(III) complexes of the form [Ir(C^N)2(N^N]PF6 (C^N is a cyclometalating ligand, N^N is a diimine ancillary ligand).
Excited state self-quenching during the operation can limit the lifetime of the device. A strategy to circumvent this issue is to decorate the Ir-complexes with bulky, hydrophobic substituents that increase the intermolecular distance while also hindering the disadvantageous attack of small molecules. For example, introduction of bulky substituents on the N^N ligand leads to more stable LEECs [2, 3].
In this context, we will present a new family of cationic Ir(III) complexes [Ir(C^N)2(dtBubpy)]+ in which bulky substituents R1 and R2 have been incorporated onto the C^N ligands. We will show the impact of the steric bulk on their photophysical properties.

Iridium complexes have received much attention for organic-light emitting diode (OLED) applications. The strong spin-orbit coupling of iridium enables efficient intersystem crossing so that emissions from both singlet and triplet states can be utilized. The vast majority of iridium complexes for OLED applications are mononuclear with facial tris(2-phenylpyridine)iridium [Ir(ppy)3] and its derivatives being the most widely used. However, mononuclear iridium complexes are complicated by the presence of meridional and facial isomers whose photophysics, stabilities and electroluminescence performance are markedly different. Scrambling of ligands is possible in the preparation of mononuclear heteroleptic iridium complexes. Furthermore, the preparation of fac-triscyclometallated iridium complexes requires very high reaction temperature or solventless reactions involving excess ligands during which decomposition of the product complexes may result.

In this study, a series of chloro-bridged iridium dimers with formylated ligands have been prepared and their photophysics and electrochemistry are studied. The aforementioned problems of mononuclear iridium complexes are all absent. More importantly, a very preliminary yet efficient OLED device using one of the dimers, [Ir(3-CHO-fppy)2Cl]2, as dopant gave a decent EQE of 2.6% which closely matches the best OLED device using chloro-bridged iridium dimers as emitter reported. The major values of this study are that we have shown chloro-bridged dinuclear iridium complexes can be a general approach for OLED applications and that this study challenges the traditional view that dinuclear iridium complexes cannot be a good OLED material.

20th International Symposium on the Photophysics and Photochemistry of Coordination Compounds, 08/07/2013, Traverse City, MI, USA

One of the longstanding challenges in the design of electroluminescent devices such as light-emitting electrochemical cells (LEECs) is the development of a bright true-blue emitter and a resulting device that is stable at low operational voltages. Herein, I will present our recent efforts to rationally address this issue and highlight several lead complexes that emit in solution and in the solid state with λmax < 500 nm. Finally data from blue-emitting LEECs will be presented.

A huge number of mononuclear Ir(III) organometallic complexes has been developed recently for visual display applications such as light-emitting electrochemical cells (LEECs). Their incorporation into LEECs is particularly attractive due to their high quantum efficiencies and their thermal and chemical stabilities. Dinuclear iridium complexes are a far less explored category of luminescent materials. Herein, we present dinuclear complexes incorporating a 2,5-di-(2-pyridyl)pyrazine ligand. The properties for these complexes are contrasted with mononuclear model systems. Electrochemical and photochemical properties will be discussed and these results will be compared to DFT studies.

Efficient white light devices are of particular interest for large scale lighting applications. Herein, we report our efforts towards the synthesis of hybrid Pt-Ir-containing organometallic polymers with the goal of obtaining high performance luminophores for WOLED applications. As a first step towards polymer construction, we report the synthesis of a series of homometallic and heterometallic monomeric units. An overview of the synthesis and detailed photophysical characterization of the polymer and there model monomers is reported.

Understanding of the behaviour of matter on the molecular level allows for major advancements in materials design. The challenge is to predict physical proprieties of a macroscopic system based on tiny structural changes on the molecules that compose this system. Liquid crystals are ideal materials to investigate the correlation between molecular structure and physical proprieties since the emergence of mesophases are highly dependent on molecular structure and intermolecular interactions. This project focuses on two structural parameters of a series of sulfinate-based calamitic liquid crystal homologues. We are interested in probing the influence of these parameters over the thermal stability of the smectic C (SmC) phase. The first parameter is the relative orientation of internal and peripheral dipoles within the molecules. The second is the length of the aliphatic chains on both sides of the mesogen. This study will be done by plotting binary phase diagrams using differential scanning calorimetry (DSC). X-rays diffraction and polarised light microscopy will then allow us to elucidate liquid crystalline polymorphism. Ultimately our goal is to use our find to dictate the design of new ferroelectric liquid crystals for non-linear optic applications.

19th ISPPCC, 03/07/2011, Strasbourg, France

The Determination Of The Role and Propertoes Of 1,2,3-Triazoles As Pyridine Mimics. Incorporation Into Phosphorescent Iridium(III) ComplexesView PDF

For decades, the pyridine moiety has been used in the coordination of metallic species for various applications. In order to discover phosphorescent molecules with improved properties that can be incorporated into materials from OLEDs to solar cells, new ligand architectures need to be investigated. This presentation will focus on the synthesis and the photophysical and electrochemical characterization of charged and neutral iridium complexes containing a far less studied heterocycle in coordination chemistry; the 1,2,3-triazole moiety [1]. These complexes will be compared to their pyridine homologues.

The type of ligands under investigation are 1-benzyl-4-(aryl or pyridyl)-1H-1,2,3-triazoles (phtl and pytl, respectively). The 1,2,3-triazoles were easily obtained via our one-pot modification of the classical “click reaction” protocol [2]. Complexation with a source of Iridium(III) afforded heteroleptic charged and homoleptic neutral complexes.

The photophysical and electrochemical properties of the complexes were analyzed together with computational modeling in such a way as to establish a structure-property relationship. These triazole ligands caused a blue shift in the phosphorescence energy and a large increased quantum efficiency compared to their pyridine homologues. Preliminary OLED fabrication data based on these complexes will also be presented.

The interest of the hemicage (HC) structure, employing a 1,3,5-trisubtituted benzene scaffold, is through the pre-orientation of its “arms” in the presence of an analyte. Like active sites of enzymes, these constructs can trap small organic molecules or metals. By themselves, the HC ligands under investigation are fluorophores and the incorporation of a metal analyte (e.g., Ru, Ir) changes greatly the absorbance and fluorescence properties of the adduct. The large changes in these properties make the material a potential sensitive detector of metals. The HC serves as our model compound for the study of the bis(hemicage) (BHC). With the additional complexation site, the BHC can complex up to two analytes. The cyclophane plays two roles: it's a good chromophore and fluorophore; it mediates electronic communication from one side of the cyclophane to the other. The BHC can thus be seen as a logic gate. The current report shows the synthesis and photophysical analysis of the HC model system and our efforts toward the construction of the BHC.

3e Colloque CQMF, 07/08/2010, Orford, Québec, Canada

Discovering new Pt, Ir organometallic complexes and their applications in OLEDs View PDF

OLEDs are light-emitting diodes (LED) in which the emissive electroluminescent layer is a film of organic or organometallic compounds. The manufacturing process of OLED lends itself to several advantages over flat-panel displays made with LCD technology, notably cheaper and more energy efficient displays. Highly luminescent platinum and iridium complexes have each been examined as lumiophores in solid state OLED technology. Herein, we report our efforts towards the synthesis of hybrid Ir-Pt-containing organometallic polymers with the goal of obtaining high performance luminophores for WOLED applications. As a first step towards polymer construction, we report the synthesis of a series of homometallic and heterometallic monomeric units. 5,5' ethnyl-2,2'-bipyridine derivatized units were synthesized using Negishi and Stille coupling reactions. They were then coupled with Pt(PBu3)2Cl2 to afford Pt-acetylide containing complexes. Finally, these molecules were coupled with a dimeric iridium source. An overview of the synthesis and initial photophysical characterization of the model monomers will be reported.